Apparatus for burning high viscosity liquid fuels

ABSTRACT

A furnace for burning highly viscous combustibles in which the materials are sprayed into a preheated combustion chamber. The spraying device has a fuel-spraying nozzle which is associated with an annular discharge nozzle for spraying medium such as compressed gas, steam, etc. The spraying medium combines with the fuel exteriorly of the nozzle and is combined with primary air combustion air. A device is provided for spraying secondary air in the direction for accelerating the sprayed stream of fuel to sweep the refractory wall within the furnace for effecting complete combustion of any unburned particles deposited therein. The exhaust gases are discharged through a flue into a remote heat exchanger for recovering the heat of combustion prior to passage through the stack.

United States Patent Sakata et a1.

Assignees:

APPARATUS FOR BURNING HIGH VISCOSITY LIQUID FUELS Inventors: Masanobu Sakata; Yoji Kitaoka,

both of lchihara; Nobuo Itami, Okayama; Yoshitada Tomoyasu, Tamano, all of Japan Mitsui Shipbuilding and Engineering Co. Ltd.; Petrochemical Industries Limited, Tokyo, Japan Filed: May 10, 1972 Appl. No.: 251,872

Related U.S. Application Data Division of Ser. No. 57,242, July 22, 1970,

abandoned. g g Y M Foreign Application Priority Data May 8, 1970 Japan ..45/39449 US. Cl 431/190, 431/115, 431/174 Int. Cl. F23c 7/02 Field of Search 431/190, 115, 116,

- References Cited UNITED STATES PATENTS 12/1929 Jackson 431/190 X 5/1949 Feinberg 431/19 3,179,150 4/1965 Arnold 431/190 2,591,188 4/1952 Nilsson 431/190 X 3,237,677 3/1966 Wiesenthal et al.

2,062,749 12/1936 Hartwig 43l/l794n 620,752 3/1899 Dorenfcldt 122/7 C Primary Examiner-Edward G. Favors Attorneyl-iowson & Howson 5 7 ABSTRACT A furnace for burning highly viscous combustibles in which the materials are sprayed into a preheated combustion chamber. The spraying device has a fuelspraying nozzle which is associated with an annular discharge nozzle for spraying medium such as compressed gas, steam, etc. The spraying medium combines with the fuel exteriorly of the nozzle and is combined with primary air combustion air. A device is provided for spraying secondary air in the direction for accelerating the sprayed stream of fuel to sweep the refractory wall within the furnace for effecting complete combustion of any unburned particles deposited therein. The exhaust gases are discharged through a flue into a remote heat exchanger for recovering the heat of combustion prior to passage through the stack.

1 7 //x a I I 0 QM 86 4 E f ////////,///////////i a APPARATUS FOR BURNING HIGH VISCOSITY LIQUID FUELS This is a continuation, divisional, of application Ser. No. 57,242 filed July 22, 1970 and now abandoned.

This invention relates to an apparatus for burning highly viscous combustibles such as low co-polymers which are produced on polymerization of olefins in the petrochemical industry.

Heavy oil or tar usually used as liquid fuel is vaporized or atomized by means of air or water vapour for burning more easily. Particularly, when burning a large quantity of such fuels, the latter process is generally employed. For atomizing fuel, there are used various processes such as rotary system, atomization under pressure, and atomization by water vapour or air, and in each process fuel is pre-heated to reduce its viscosity down to an adequate level for atomization (generally l ettha qssiwheaqs asmi wis mba ibles such as lower co-polymer-by-products, however, viscosity adequate for the above-described burners of conventional types cannot be obtained by heating, and when heating excessively, the materials are cracked to gasify or deposit carbon before the viscosity reduces to an adequate level, thus they cannot be transferred by a normal way. The fuels of this type cannot be atomized sufficiently to be completely burned by conventional burners, and accordingly, it is very hard in practice to burn such fuels only due to atomization. As it takes some time to fire sprayed fuel having large particle size, flames are hardly maintained by a so-called flamepropagation system wherein combustion velocity balances with spraying velocity. Even if flames can be maintained such as by using flame-maintaining means, it takes a long time to burn fuel of large particle size completely in a furnace cavity, thus there is required a very long residence time for assuring to keep the said time, and therefore, a large combustion furnace is necessitated. It is not advantageous in practice. Furthermore, if combustion heat is taken away by some external substances from fuel particles during combustion, the combustion temperature is hardly raised up sufficiently, and it results in incomplete combustion and production of carbon residue, which deposits and accumulates on the furnace walls to inhibit continuous combustion.

According to the reasons described above, it has not been practised heretofore to burn such fuels by an atomization process, and it has been considered to be very hard to burn large quantities of such fuels as heat sources for commercial boilers and the like.

This invention provides an apparatus which can burn large quantities of high viscosity fuels such as lower copolymer-by-products completely and continuously and recover the heat from the fuel gases with boilers and the like.

Another object of this invention is to provide a combustion apparatus provided with a fuel spraying means which can atomize highly viscous liquid fuel sufficiently.

The apparatus of this invention consists of means for spraying high viscosity liquid fuel into a combustion furnace, a combustion furnace for burning the sprayed fuel, and means for recovering the heat from combustion gas in the combustion furnace. The main object of the fuel spraying means is to atomize fuel as fine as possible and spread it homogeneously in a furnace. The shape, number, amount and the location of the spraying means are properly selected depending on the size of the furnace and the amount of the fuel. In accordance with the present invention the fuel is atomized by means of highly compressed air or water vapour when sprayed from the nozzle.

Fuel is atomized as much as possible by the said spraying means, and sprayed fuel particles of smaller than a certain particle diameter are expected to be burned in a combustion space. The inside wall of a combustion furnace is all lined with insulating and refractory materials. The temperature of the inside wall surface of the furnace is kept at higher than the ignition temperature and the combustion temperature of fuels: the fuel charged into the furnace is immediately heated up at the combustion temperature by the radiant heat of the wall, and mixed under diffusion with air which is blown into together therewith, the fuel is thus partially burned in primary combustion in a combustion space. The rest of the fuel which has not burned in the combustion space diffuses to deposit on the furnace wall and is further heated by the wall, so that the fuel burns completely in surface combustion.

Generally, the surface combustion velocity of fuel is determined by a surface temperature and a flow velocity of air passing over the said surface, the higher the temperature is and the larger the flow velocity of the air is, the larger the combustion velocity becomes. In the combustion furnace in accordance with the present invention, air is divided into a primary air and secondary one. The primary air is injected into the furnace from the same place as fuel at high velocity and at a moderate angle with the horizontal plane. The secondary air is injected into the furnace from the opposite wall near the furnace bed in the direction in order to accelerate the gas circulation in the furnace thus combustion gas circulates in the furnace at high velocity. In accordance with this process, not only fuel and air are diffused and mixed together more effectively in a combustion space, butalso the air passes with high velocity over the fuel attaching on the furnace wall which results in raising the surface combustion temperature of the fuel and reducing the size of a furnace. For keeping a furnace wall at high temperature, the inside of the furnace is completely separated from a cooling surface to recover the heat of the combustion gas and from an air opening to the outside, and the furnace is designed to have a capacity enough to keep a sufficient residence time for complete combustion of fuel. Designing the furnace as described above, the combustion temperature can be well kept till combustion is completely finished, and soot and black smoke are never generated as long as air is sufficiently supplied. The completely burned and high-temperature combustion gas is introduced to a heat recovering means through a flue. As the heat recovering means, heat exchanger such as boiler and the like may be employed.

The present invention will be better understood from the following description taken in connection with the attached drawings in which:

FIG. 1 is a longitudinal sectional view showing an embodiment of this invention:

FIG. 2 is a sectional view taken along the line A-A:

FIG. 3 is an enlarged sectional view of a fuel spraying means: and

FIG. 4 is an enlarged sectional view showing another embodiment of a fuel spraying means.

In FIGS. 1 and 2, a combustion furnace 1 is completely surrounded by an insulating and refractory wall 2, and a fuel spraying device is provided on a side of the wall downward. On the opposite side of the wall, a secondary air-blowing nozzle 12 is located. FIG. 3 shows the construction of the fuel spraying device 10; in a primary air-blowing tube 9, tubes 17 and 18 are provided concentrically, and fuel is introduced through the central tube 17 and supplied from a nozzle 19 into the furnace. Through the gap between the tubes 17 and 18, highly compressed water vapour or air as a fuelspraying medium is transferred and sprayed from a nozzle 20.

The critical pressure in the tube 18 for a highly compressed gas is selected higher than the pressure in the furnace l. The fuel is atomized primarily due to the relative velocity of the fuel sprayed from the nozzle 19 and the spraying medium sprayed from the nozzle 20.

When the fuel introduced through the tube 17 is heated at high temperature to reduce the viscosity, it should be prevented to be cooled during passing the tube 17. Therefore the highly compressed gas passing the tube 18 is of preferably highly compressed water vapour for keeping the temperature of the fuel passing through the tube 17. When fuel is not necessary to be kept at high temperature, a cold highly compressed air may be supplied for spraying fuel. The highly compressed gas is sprayed from the nozzle 20 in the direction to cross the spraying direction of fuel from the nozzle 19 in order to effectively use the momentum of the highly compressed gas for atomization of fuel. Such atomizers of a highly compressed gas spraying means generally employ an internal mixing method, but when using the internal mixing method for atomization of high viscosity fuel, the spraying nozzle portion is clogged with fuel, and consequently a homogeneous spraying stream cannot be obtained; thus, good atomization cannot be attained. In the present invention, therefore, an external mixing method is employed for getting good atomization of fuel, as described above.

A part or all of the primary air for combustion is sprayed from a ring-shaped nozzle 16 through a tube 9. The air is injected in the direction across the flow of fuel sprayed primarily from the nozzle 20 by means of the highly compressed gas so as to further atomize it most effectively. The spraying velocity is selected at 70 to 200m/sec., for instance, and the fuel atomized by the highly compressed gas is atomized secondarily by the momentum of the air.

Ignition on starting the operation is performed by heating the furnace l by an adequate device. The circulating flow of the furnace gas is accelerated by reciprocal action of the sprayed flows from the tubes 9 and 12, and fuel is completely burned in the furnace cavity and on the surface of the refractory wall. Fuel particles smaller than a predetermined particle diameter are completely burned before they reach the walls 14 and 15 or in the stream 13, while the particles having the larger diameters are spread to attach on the walls 14 and 15, where they are quickly vaporized by the heat of the walls and exposed to a high speed stream to be burned with a very high combustion velosity. As the furnace wall is kept at a sufficiently high temperature by the combustion heat of fuel, the fuel attaching on the wall is burned without producing carbon residue. Further, as the temperature in the furnace is kept at very high level, if adequate residence time and an adequate oxygen are given in the furnace, soot and smoke are not produced.

The combustion gas passes through a flue 4 and is introduced to a heat exchanger 6, where heat recovering is performed, then exhausted out of a funnel 7. The wall 2 of the combustion furnace 1 should be kept at temperatures at which combustion is performed quickly enough all over the surface, for instance, at l,O00-l,200 C. Therefore, the heat exchanger 6 is completely separated from the furnace 1, only connected with the flue 4 in order that fuel which is not burned completely is entirely prevented from coming in contact with a cold wall surface of the heat exchanger. It is recommended to provide a barrier 3 to prolong the residence time of combustion gas as long as possible in the furnace, so that the inside of the furnace is cooled by the heat radiation to the heat exchanger 6. For distributing the sprayed fuel in the furnace as uniformly as possible, more than one fuel spraying device is disposed along the longitudinal direction, and in this example three devices are employed.

FIG. 4 shows another example of the fuel spraying device. In this example, a high viscosity fuel is charged through a tube 21 and sprayed from a ring-shaped nozzle 23 through a tube 22. A highly compressed gas for spraying is injected from a ring-shaped nozzle 25 through a tube 24. According to such a design, high viscosity fuel can be sprayed as a very thin layer, and thus, a comparatively large quantity of fuel can be well atomized by one spraying device. The primary air of low pressure is injected from a nozzle 28 through tubes 26 and 27, similar in the example of FIG. 3, and atomization is satisfactorily performed by reciprocal action together with the gas of high pressure sprayed from the nozzle 25. When all of the combustion air is not sprayed from the nozzle 28, the rest of the air is charged through an air way 29, and introduced into the furnace 1 through an air box 30 and a burner throat 31. The air is circulated, if necessary, by fins 32, and the sprayed fuel is quickly mixed with air.

According to the present invention, large quantity of very high viscosity fuels such as low polymers produced on polymerization of olefms in the petrochemical industry can be completely burned, and also the waste heat can be recovered.

We claim:

1. An apparatus for burning high viscosity liquid fuels, characterized by a horizontally-elongated furnace having a combustion space defined by an insulating refractory wall capable of being heated above the ignition and combustion temperature of the fuel, and being provided with fuel-spraying devices disposed in a wall along the longitudinal direction of the furnace, each of said devices having a fuel-spraying nozzle and a primary-air nozzle provided near the said fuelspraying nozzle and spraying a flow of primary air in the direction across the spraying direction of said fuelspraying nozzle, the fuel-spraying device being located so as to spray a stream of fuel and primary air toward the bottom of the furnace, and further provided with secondary air spraying devices disposed in a wall opposite said fuel spraying devices, and a flue at the longitudinal end of the furnace, the secondary air spraying devices spraying a flow of secondary air in the direction for accelerating the sprayed stream of the fuel and primary air, said spraying devices being arranged for circulating the stream of fuel along the refractory wall with centrifugal force whereby unburned particles are deposited on said wall to effect complete burning of said deposits on the surface of the wall.

I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,779,-69l Dated December 18, 1973 Inventor(s) Masanobu Sakata et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading under the list of inventors, the following three inventors should be listed:

-- 'Kazuhiko Shibayama, Ichihara; Kunio Furutachi;

l'wa-kuni; and Hideo Mineshima, Ichihara.-

In the heading under Assignees, the second assign ee should be identified as follows:

- -Mits1ii Petrochemical InduStries'Li mited- Signed and seal ed this 10th day of September 197 E Attest: I McCCY M. GIBSON, JR. l c. MARSHALL DANN Q Attesting Officer Commissioner" of Patents UscoMM-Dc 603764 69 U.5. GOVERNMENT PRI NTINQS OFFICE: I939 0-36-33,

FORM PO-105O (10-69) 

1. An apparatus for burning high viscosity liquid fuels, characterized by a horizontally-elongated furnace having a combustion space defined by an insulating refractory wall capable of being heated above the ignition and combustion temperature of the fuel, and being provided with fuel-spraying devices disposed in a wall along the longitudinal direction of the furnace, each of said devices having a fuel-spraying nozzle and a primary-air nozzle provided near the said fuel-spraying nozzle and spraying a flow of primary air in the direction across the spraying direction of said fuel-spraying nozzle, the fuel-spraying device being located so as to spray a stream of fuel and primary air toward the bottom of the furnace, and further provided with secondary air spraying devices disposed in a wall opposite said fuel spraying devices, and a flue at the longitudinal end of the furnace, the secondary air spraying devices spraying a flow of secondary air in the direction for accelerating the sprayed stream of the fuel and primary air, said spraying devices being arranged for circulating the stream of fuel along the refractory wall with centrifugal force whereby unburned particles are deposited on said wall to effect complete burning of said deposits on the surface of the wall. 